Towards gas-phase electron diffraction of novel species

Novel additions have been made to the York time-averaged electron diffractometer with a view to the study of low volatility and more exotic species. The telefocus electron gun present in the apparatus has been improved and the resulting beam width reduced from 0.76 to 0.40 mm. The existing data collection system was fully tested and eventually replaced with a custom designed camera
assembly to improve data quality; this was further improved by the addition of a liquid nitrogen cold trap.

For the study of lower-volatility compounds an air-heated nozzle assembly was built, which, paired with the high intensity of electrons produced from the telefocus gun and almost limitless data acquisition possible using the camera assembly, allows diffraction patterns to be collected from a smaller target density in the sample beam.

Molecular dynamics simulations have been performed using Newton-X to provide vibrational corrections for refinements. These corrections allow a better description for large-amplitude and anharmonic motions, which are badly accounted for using current methods. These will be especially useful for the more complex molecules the apparatus has been designed to study.

To extract and handle the diffraction data collected, custom software has been developed and tested. This software, combined with the improvements and additions to the apparatus, was used to refine the structure of 4-(dimethylamino)benzonitrile.

The combination of these improvements to the apparatus and the custom software, will allow the structure determination of species such as carbon suboxide (C 3 O 2 ), and silyl chloride (SiH 3 Cl) dimers.